Appliance sizing · India
A 1.5 ton air conditioner uses roughly 8–13 units a day in normal use, which points to about 2.5–3 kW of rooftop capacity. But a grid-connected plant does not run your AC — it reduces the units you are billed for. That difference changes the answer, especially if you cool your rooms at night.
Rough arithmetic
Indicative daily consumption and the capacity that offsets it across a year. Star rating, thermostat setting, room insulation and outdoor temperature move these figures a lot.
| AC | Typical running draw | ~8 hrs/day | Capacity to offset |
|---|---|---|---|
| 1.0 ton, inverter | ≈ 0.8–1.1 kW | ≈ 6–9 units | ≈ 1.5–2 kW |
| 1.5 ton, inverter | ≈ 1.1–1.6 kW | ≈ 8–13 units | ≈ 2.5–3 kW |
| 1.5 ton, non-inverter | ≈ 1.5–1.8 kW | ≈ 11–15 units | ≈ 3–3.5 kW |
| 2.0 ton, inverter | ≈ 1.5–2.0 kW | ≈ 11–16 units | ≈ 3–4 kW |
| Two 1.5 ton units | — | ≈ 16–26 units | ≈ 4–6 kW |
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The phrase "panels to run the AC" pictures a wire from the roof to the appliance. That is not how a grid-connected rooftop system works. Panels feed an inverter, the inverter feeds your home's supply as a whole, and any surplus goes out to the grid. Your AC, fridge and lights all draw from the same pool. There is no configuration in which one appliance is on solar and another is not.
So what the plant genuinely delivers is fewer billed units. Which means the right unit of measurement is not panels-per-appliance but units per month — and that is a number your electricity bill already reports. Everything below is really about translating a cooling habit into units so you can check it against that bill.
Air conditioners in Indian homes are used most heavily in the evening and overnight. Rooftop solar generates in the middle of the day. Those two curves barely overlap.
Under net metering this is not fatal: your daytime surplus is exported and credited against the units you import after dark. But a credit is generally worth less than the retail unit it replaces, because export is settled at a rate set by your state's tariff order rather than at the slab rate you would otherwise pay. The mechanics are in net metering in India.
The practical consequence is worth stating plainly. Two households with identical bills and identical 3 kW systems can see noticeably different savings purely from when the cooling happens. A family cooling living rooms through hot afternoons consumes much of the generation directly at full tariff value. A family that only cools bedrooms from 10pm exports nearly all of it and buys it back at a worse rate. Nobody selling you panels is likely to raise this, and it is the difference between a good and a mediocre outcome on the same hardware.
If your cooling is mostly nocturnal, the free improvement is to move whatever is flexible into daylight — laundry, pumping, dishwashing, vehicle charging — rather than buying more capacity.
Calculating from tonnage requires assumptions about star rating, compressor behaviour, insulation and how low you set the thermostat. You can skip all of it, because your meter has already measured the answer.
Compare the units on a peak-summer bill against a mild month such as February or November. The difference is your actual cooling load — measured on your home, your habits and your rooms rather than estimated. Do it across a full year if you can, since most Indian homes have two or three genuinely heavy months and a long tail of light ones.
That annual figure is what should drive sizing. Ask any installer what annual generation their payback claim assumes and how they derived it; a quote built on peak-summer consumption will recommend a bigger plant than your year justifies.
If you size for your hottest weeks, you own that capacity for the other eight or nine months too. In those months the extra generation is surplus, and surplus settles at export rates rather than saving you full tariff. You have bought peak-summer capability at full price and it earns the weaker rate most of the year.
There is a second trap in the same direction. Central assistance stops rising after 3 kW, so capacity added to chase a summer peak is unsubsidised — the fourth and fifth kilowatts can cost nearly twice as much each as the first three. That arithmetic is worked through in 3 kW vs 5 kW.
Solar also settles over a year rather than a month. A winter surplus can partly fund a summer shortfall depending on your state's settlement rules, which is another reason annual units beat peak units as the sizing input.
Sanctioned load. Printed on your bill. Heavy AC use sometimes means a household is already close to it, and if the plant capacity you apply for exceeds the sanctioned figure many distribution companies require a load enhancement with its own charge and queue, outside the installer's quotation.
Shadow-free roof. Plan on roughly 8–10 m² per kilowatt plus space to walk around the array for cleaning. Once the water tank, stair room and parapet shadow are accounted for, the roof frequently caps the size before the budget does.
That is a different purchase and should be priced separately. A standard grid-tied plant shuts down in an outage as a safety requirement, so it contributes nothing exactly when the power is off. Running air conditioning on batteries is materially more expensive than keeping lights and fans alive, because cooling is a heavy sustained load. The options are compared in on-grid vs off-grid vs hybrid.
For a single 1.5 ton inverter AC in typical use, 2.5–3 kW is the right order of magnitude, and for most Indian homes a 3 kW plant is the sensible landing point anyway because that is where central assistance peaks. But confirm it against twelve months of units instead of an appliance label, and be realistic about when your cooling happens — that timing affects your return more than one extra panel ever will.
Run the free home check from your bill and we will size it from your real units. If your reason for asking is running the AC through a power cut, that needs storage rather than more panels — see solar battery price. Related: 3 kW price · 2 kW price · costs & payback · ₹3,000 bills.
A 1.5 ton unit typically draws somewhere between 1.1 and 1.6 kilowatts while the compressor is working, so eight hours of use lands roughly in the 8 to 13 units a day range depending on star rating, thermostat setting, insulation and outdoor temperature. Offsetting that over a year needs broadly 2.5 to 3 kilowatts of rooftop capacity, which at current module sizes is around five to eight panels. Treat that as an order-of-magnitude answer, because the honest sizing comes from your bill rather than from the appliance.
Not in the way the question implies. A standard grid-connected rooftop plant does not power individual appliances; it feeds your home's supply and pushes any surplus to the grid, so what it really does is reduce the number of units you are billed for. There is no wiring in which your AC is on solar and your fridge is not. If you want an appliance to keep running during a power cut, that is a storage question rather than a panel-count question.
It helps, but less than the panel-count arithmetic suggests, and this is the single most important caveat on this page. Your plant generates during the day and your AC consumes after dark, so you export by day and import by night. Under net metering that exported energy earns a credit against your imports, but a credit is generally worth less than the retail unit it replaces. So a household cooling bedrooms overnight gets a weaker return than one cooling living areas through the afternoon, even with an identical bill and an identical system.
Multiply the running power in kilowatts by the hours you use it. A 1.5 ton inverter unit at around 1.2 kW for six hours is roughly 7 units a day. But the reliable figure is already in your hand: compare your electricity bill units in peak summer against a mild month. The difference is your real cooling load, measured on your home rather than estimated from a specification sheet, and it already accounts for your thermostat habits and how well your rooms hold cool air.
No. Size it from twelve months of units on your bill, which already includes the AC along with everything else. Sizing around one appliance tends to produce a plant matched to your hottest weeks and oversized for the other eight months of the year, and surplus generation settles at export rates rather than saving you full tariff. Annual units, not peak-summer units, is the correct input.
Often it covers a meaningful share of both, but it depends on your total consumption rather than on the AC alone. A 3 kW plant generates broadly 360 to 450 units a month, planning conservatively. If your annual average is near that figure, 3 kW is a sensible fit and it is also where central assistance reaches its ceiling. If summer pushes you far above it while winter sits far below, remember that solar settles across the year, so the winter surplus partly funds the summer shortfall.
Only if your goal is running the AC during a power cut, which is a different purchase from lowering your bill. Batteries sized to carry air conditioning through an evening are substantially more expensive than ones that keep lights and fans going, because cooling is a heavy sustained load rather than a small one. For bill reduction alone, a grid-connected plant without batteries is the cheaper and usually correct choice.
